Control of selecting magnets in crossbar switches



Nov. 3, 1959 c. G. SVALA ET AL 2,911,479

CONTROL OF SELECTING MAGNETS IN CROSSBAR SWITCHES Filed Sept. 26, 1956 s Sheets-Sheet 1 Fig. 2

/A I N new rqR s Cmu GaIvN/IR 61 91 Afwn Gwv/vm? BRU/VBERG Br HM wwf/ Nov. 3, 1959 c. G. SVALA ET AL CONTROL OF SELECTING MAGNETS IN CROSSBAR SWITCHES 3 Sheets-Sheet 2 Filed Sept. 26, 1956 l (I m 2 K M M O 1 2 45 6 w. w mm m, o T I73. W l E u :2: 1 J C M V L! 6., n G V 4 2 +8 2 W 4 4 2 m m 1 L u 9 F 32.11 v Fm M FW 1 w 0 M 2 w (I lllm 23 v Y m m z. 1 uJ+D D m.

0 Z R W N MW 66 44 RR Ha CK Nov. 3, 1959 c. e. SVALA ETAL 2,911,479

I 4 CONTROL OF SELECTING MAGNETS IN CROSSBAR SWITCHES Filed Sept. 26, 1956 s Sheets-Sheet 3 {i VA 0 E T M I:!

f 011 K1 K2 l IA vE/vroRs CHRL Cum/v0? 67 1940 KQ/u Cum/me BRl/A/EERG BY MW United States Patent CONTROL OF SELECTING MAGNETS IN CROSS- BAR SWITCHES Carl Gunnar Svala, Alvsjo, and Karl Gunnar Brunberg, Segeltorp, Sweden, assignors to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden, a corporation of Swe- The present invention refers to a connecting device for control of the actuation of a selecting magnet in automatic telephone systems with cross bar switches which are set from a marker by completing direct current circuits for the actuation of a selecting magnet and after that of an operating magnet. In such telephone systems the marker is expensive and it is of great importance to obtain quick switching operations inorder to reduce the busy time of the marker upon operation of'each selector. As heretofore known, each selecting magnet has been provided with a particular contact which must be closed before the operating magnet can attract,-'or a means causing a time interval of a predetermined length has been interposed between the completion of the circuit of the selecting magnet and the completion of the circuit of the operating magnet. The first mentioned arrangement entails expenses both for a contact on each selecting magnet and for conducting wires between said contacts and the marker and expenses for the connection of said wires to the marker. The last mentioned arrangement causes a loss of time, as the selecting magnets are unequal in relation to each other and as a safety margin is necessary. Neither arrangement can be safely controlled so that the selecting magnet attracts its armature.

According to the present invention the actuation of the selecting magnet iscontrolled without additional contacts and without additional conducting wires and Without any loss of time. This is achieved by associating a transformer with the marker. The primary winding of the transformer is connected to the make-circuit of the selecting magnet and the secondary winding is-connected to an indicator. The indicator is actuated by the change in current caused by the induction in the circuit of the bar magnet, when the armature of the selecting magnet is attracted, the circuit of the operating magnet being completed by the actuation of said indicator.

The invention will be described more in detail in connection with the attached drawings. a 7

Figs. 1-3 show the current and voltage phenomena in the windings of the transformer.

Fig. 4 shows an embodiment of the invention; a discharge tube and a relay being used as an indicator;

Fig. 5 shows another embodiment of the invention, a transistor and a relay being used as an indicator.

Fig. 1 shows how the current in a selecting magnet increases. At the point Q the armature of the selecting magnet starts to move and at the point P the armature strikes against the core of 'tliemagnet. During the movement of the armature themagnetic field in the core is increased inducing an oppositelydirected'electromotive force which reduces the current through the winding of the selecting magnet and through the primary winding of the transformer. The voltage produced in the secondary winding of the transformer varies as shown in Fig. 2'. The curve in Fig. 2 is the first derivative to the curve in Fig. 1. Should a condenser connected in series with a suitable resistance be connected to the secondary winding of the transformer, the current through the resistance will vary according to Fig. 3. The curve in Fig. 3 is the first derivative to the curve in Fig. 2 and, thus, the second derivative to the curve in Fig. 1. The peaks UA, UB or IA, IB may actuate an indicator which indicates that the selecting magnet has attracted its armature. The current impulse IC in Fig. 3 is caused by eddy currents and charging currents to winding capacities and it appears at the connection instantly. If the bar magnet has a large pole stud and small movement, the peaks UA and IA may, however, disappear, the current curve in I Fig. 1 and the voltage curve in Fig. 2 having the form indicated by dashed lines. At first a device will therefore be described by means of Fig. 4, said device being based upon the current impulse IB. Current impulses IB in Fig. 3 arise when the armature of the selecting magnet strikes against the core of the selecting magnet. The voltage, in Fig. 2 induced in the secondary winding of the transformer changes from the value UA to the value UB during a very short time interval.

In Fig. 4, A is a telephone instrument and L a line provided with a line relay LR and an operating bar for cross-bar switches, the operating magnet BR and the circuit. For the control of the function of the selecting magnets M1-M10 there is an indicating device consisting of the transformer T, the discharge tube GL and the relays K1K2. The discharge tube GL has an initial ionization from a current source VF via a resistance r3 and has a bias voltage on the fire electrode from a current source VG via the resistances r1 and r2. As shown in the figure spring sets on the selecting magnets are required.

Upon a call from the instrument A, the line relay LR operates. The contacts 11-12 are actuated. The contacts 12 for the line relays which belong to a tens number are interconnected. The relay' D1 is energized via.

the contacts 12 and 403 and operates. The contacts 101-105 are actuated. Each one of the contacts 11 for the line relays in the tens number is connected to its contact 104-105 on the tens relay D1. The relays D11 and V10 operate in the following circuits: the contact 10-3, the coil of the relay D11 to negative, respectively, the contacts 395-305, 424, 303, the coil of the relay V10, the contact 31 to negative. The contact 31 is closed, when the link circuit SN is idle. The con tacts 400-403 and 301-306 are actuated. The relay D1 is then kept energized through the contact 101. The relay N2 in the link circuit SN operates in a circuit through the contact 306. The contact 32 is closed and The contact 33 is closed. The relays :U1-U10 form a relay chain'in which only one" relay at a time can operate; The relay U1 operates at the relay N3 operates.

Patented Nov. 3, 1959,

the same time as the relay V10 in the following circuit: the contacts 201-291, the contact 203, the upper and the lower windings of the relay U1, the contacts 104 and 11, the winding of the operating magnet BR, to negative. The upper coil of the unit relays Ul-U10 has such a high resistance, that the operating magnet BR cannot operate in series with the same.

The contact 301 closes before the contact 302. The following two circuits are formed:

(a) the contact 301, the coil of the relay K1, to negative,

(b) the lower winding of the transformer T, the contact 302, the selecting magnet M10, to negative.

The relay Kl operates and the contacts 411-412 are actuated, the discharge tube GL being interconnected. During the actuation of the relay K1 the current impulse IC in Fig. 3 and current impulses, if any, caused by the contact vibrations in the contacts 301-302 have time to pass the contact 412 without actuating the discharge tube GL. The current through the lower winding of the transformer T increases according to Fig. 1 and the current through the upper winding of said transformer passes through the rectifier E charging the condenser C. When the selecting magnet M10 attracts its armature M10A, the increase in current ceases and generally changes to a decrease in current IA in Fig. 3, and changes, thereafter, quickly to a current impulse 1B which passes the resistance R causing a discharge of the condenser C. The potential drop through the resistance R fires the ignition gap of the discharge tube GL, the main gap thereafter being fired and a circuit being formed through the upper winding of the relay K2 and the contacts 400, 422, and 401. The contacts 421424 are actuated. The relay K2 is thereafter kept energized through its lower winding through the contacts 411, 421 and 401. The operating magnet BR operates in the following circuit: the contacts 423 and 204, the lower winding of the relay U1 having a low resistance, the contacts 104 and 11, the Winding of the operating magnet BR, to negative. The contacts 21-22 and a, b, c are actuated. The line relay LR releases its armature and the identifier D is disengaged. The operating magnet BR is kept energized and the relay N1 operates in a circuit through the contacts 33 and c. The feeding relay N2 is kept in a circuit through the contacts a, b, the line L and the instrument A.

The object of a resistance r4 shunting the lower Winding of the transformer T is to attenuate the oscillations which easily arise when the contact 412 is actuated.

Fig. 5 shows an embodiment of the invention, the voltage peak UA in Fig. 2 actuating the indicator. The indicator according to Fig. 5 consists of a transistor S and a relay K2 and replaces the discharge tube GL and the relay K2 in Fig. 4. As in Fig. 4, a battery VA is connected to the indicator by the contact 400 on the relay D11. The selection relay V connects the selecting magnet M10 in series with the lower winding of the transformer T by means of the contacts 30130'2. During the actuation of a relay K1 contact vibrations, if any, are to be finished, said relay connecting the transistor S to the upper winding of the transformer T. In the rest position the emitter of the transistor receives a negative bias voltage from a battery VF.

When the current through the selecting magnet M10 and the lower winding of the transformer T increases, a voltage is induced in the upper winding of the transformer. Said voltage causes a current through the rectifier E and, therefore, does not actuate the transistor. When the selecting magnet M10 attracts its armature, the direction of the voltage in the upper winding of the transformer T is changed. The rectifier B does not admit current in this direction, but the voltage UA in Fig. 2 changes the bias voltage on the emitter of the transistor, so that a current arises through the contact 411, the lower winding of the relay K2 and through the wi t??? 4 of the transistor. Owing to this a circuit is closed from the battery VA, through the contacts 400 and 422, the battery VF, the transistor S and the upper winding of the relay K2. The current through the upper winding of the relay K2 induces a voltage into the lower winding of the relay K2, and said voltage increases the current in the emitter-circuit and, thus, causes a feed-back. The current intensity through the transistor and the upper winding of the relay K2 quickly increases so that the relay K2 attracts its armature. The contacts 421423 are actuated, the transistor being disconnected and the relay K2 being kept energized through the contact 421. The operating magnet BR in the cross bar switch operates in a circuit over the contact 423, said circuit being shown in Fig. 4.

We claim:

1. In an automatic telephone system comprising a cross-bar switch, lines, links and a marker for connecting said lines to said links over said cross-bar switch, operating magnets and selecting magnets having an armature in said cross-bar switch, one of said magnets associated with each line and another of said magnets associated with each link, an indicator and a transformer having a primary and a secondary winding in the marker common to all said magnets, said indicator being connected to the secondary winding of said transformer, means connecting the magnet for one of said lines to the marker, and means in the marker selecting one of said links and connecting the magnet of the selected link to the primary winding of said transformer in an operating circuit, said indicator being controlled by a change in current in said circuit due to magnetic induction upon attraction of the armature of the magnet for the selected link, the indicator when actuated operating the marker.

2. In an automatic telephone system, a cross-bar switch, lines, links and a marker for connection of said lines to said links over said cross-bar switch, operating magnets and selecting magnets having an armature in said crossbar switch, one of said magnets associated with each line and another of said selecting magnets associated with each link, an indicator and a transformer having a primary and a secondary winding in the marker common to all said magnets, said indicator being connected to the secondary winding of said transformer, means connecting the magnet for one of said lines to the marker, means in the marker selecting one of said links and connecting the magnet of the selected link to the primary winding of said transformer in an operating circuit, said indicator including a condenser and a resistance connected in series to said secondary winding and a discharge tube having an ignition gap connected in parallel with said resistance, said discharge tube being fired by the potential drop over said resistance during the increase of current immediately after the armature of the magnet for the selected link is attracted, a relay in the marker operable in response to the firing of said discharge tube for operating said marker.

3. In an automatic telephone system, a cross-bar switch, lines, links and a marker for connection of said lines to said links over said cross-bar switch, operating magnets and selecting magnets having an armature in said cross-bar switch, each of said lines and each of said links being associated with one of said magnets, an indicator and a transformer having a primary and a secondary winding in the marker common to all said magnets, said indicator being connected to the secondary winding of said transformer, means connecting the magnet for one of said lines to the marker, means in the marker selecting one of said links and connecting the magnet of the selected link to the primary winding of said transformer in an operating circuit, said indicator including a transistor amplifier, the input of which is connected to said secondary winding and an electromagnetic relay provided with a first coil connected to the output of the amplifier, a second coil on said relay comprised in the input cir- 2, 9 1 1 479 5- 6 cui-t of the amplifier and the polarity of said second coil duction when the armature of the magnet for said selected being so changed that an amplifying feed-back is received link is attracted, said relay operating the marker. from the output to the input, when the current is increased in said first relay coil, a rectifier connected over said References Cit d i th fil of hi patent secondary winding of the transformer to transmit'the 5 iced-back current but to block a current impulse incom- UNITED STATES PATENTS ing over the transformer and produced by a change in 2,733,297 Matlack et a1 Jan. 31, 1951 current in the primary winding of the transformer, said 2,744,162 Den Hertog et a1. May 1, 1956 electromagnetic relay being operable by a change in cur- 2,777,015 Jacobaeus et a1 J an. 8, 1957 rent in said operating circuit as a result of magnetic in- 10 

